Rewrite on IIS that actually works


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It is amazing to think that before IIS7 (Server 2008 / Vista) there was no native rewrite URL support for IIS.


mod_rewrite for IIS

There are many tools available to give rewrite functionality for IIS, most of which I have tried and do not work properly or do not fully support regex. The best tool I have found for the job is IIRF. Like other tools available of this type it loads through an ISAPI filter extension - but unlike others it actually works. There are a few nuances to be aware of though.


  1. Download and extract to any location eg. C:\Rewrite:
  2. Load IIS console: Start > Run > %SystemRoot%\system32\inetsrv\iis.msc
  3. Right-click 'Web sites' > Properties > ISAPI Filters > Add
  4. Type a name to recognise it by under 'Filter name' and select the IsapiRewrite4.dll file inside the lib folder of the extracted archive under 'Executable'. The filter may not appear to have loaded OK straight away, this is OK.
  5. Go to 'Web service extensions' in the right-hand pane in the main window.
  6. Click 'Add a new Web Service extension...'
  7. Type in the same details as before, ensure the allow checkbox is ticked.
  8. The config file is not created for you, the rewriter looks for a file called IsapiRewrite4.ini in the same folder as the IsapiRewrite4.dll file itself.


Example working configuration of IIRF on IIS on Windows

#Enable rewrite logging, very useful. 5 is very verbose, set to 3 unless troubleshooting.
RewriteLog  c:\temp\iirfLog.out
RewriteLogLevel 5

#redirects /misc/anything to /misctest/anything
#will not redirect /misc to /misctest due to the tailing slash
RewriteRule ^/misc/(.*)$ /misctest/$1 [I]

#Rewrite all traffic to SSL
RewriteCond %{SERVER_PORT} ^80$
RedirectRule ^/(.*)$ https://%{HTTP_HOST}/$1 [R=301]

Rewrite the base-URL (only) for a specific hostname

In Apache the first line would not be required if a vhost configuration is being used. In IIRF the rewrites cannot be encapsulated within vhosts as this configuration does not exist of course. This will rewrite the base-url (only) to when the hostname is '':

RewriteCond %{HTTP_HOST} ^www\.testing\.com$
RedirectRule ^/$ [R]

Rewrite all URLs for a domain to a holding page

A situation can arise where all URLs on a domain need to be diverted/rewritten to the same URL, such as a holding page.

RewriteCond %{HTTP_HOST} ^test\.jgpskills\.co\.uk$
RedirectRule ^/(.*)$ /

This does not cause a rewrite loop as the pattern-match is for a "/" and one or more characters but not for only the "/".

Rewrite all domains to SSL, excluding one domain

RewriteCond %{SERVER_PORT} ^80$
RewriteCond %{HTTP_HOST} ^(?!nosslsite\.company\.co\.uk)(.+)$
RedirectRule ^/(.*)$ https://%{HTTP_HOST}/$1 [R=301]

Avoid SSL certificate errors for non-canonical hostnames

If you employ a rewrite rule to force use of SSL you will find that any non-canonical/main hostnames cause an SSL certifciate error. This can be avoided by chaning together a rewrite rule with the [R] flag a visibly redirect the client to the preferred/advertised/main hostname first, before redirecting to SSL:

#Rewrite all compancyabc domains to "" before SSL rewrite to avoid cert error
#IIRF does not support proper regex so in order to catch <anything>compancyabc... I had to put
#"(^|.*)" before each condition
RewriteCond %{HTTP_HOST} (^|.*)compancyabc\.co\.uk$ [OR]
RewriteCond %{HTTP_HOST} (^|.*)compancyabc\.org\.uk$ [OR]
RewriteCond %{HTTP_HOST} (^|.*)compancyabc\.com$ [OR]
RewriteCond %{HTTP_HOST} (^|.*)compancyabc\.eu$
RedirectRule ^/($|.*)$1 [R=301]

#Rewrite everything to SSL apart from the root page and apart from demo sites
RewriteCond %{SERVER_PORT} ^80$
RewriteCond %{HTTP_HOST} ^(?!(^|.*)demo\.compancyabc\.co\.uk)(.+)$
RedirectRule ^/(.*)$ https://%{HTTP_HOST}/$1 [R=301]

Rewrite a particular URI to https

RewriteCond %{SERVER_PORT} ^80$
RewriteCond %{HTTP_HOST} ^$
RedirectRule ^/sslsite(.*)$ https://%{HTTP_HOST}/sslsite$1 [R=301]

Disable rewrite for all other URIs on a domain

#Disable all other rules for rest of the domain
RewriteCond %{HTTP_HOST} ^$
RewriteRule ^/(.*)$ /$1 [I,L]

See Also

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